1. Field of the Invention
The present invention relates to an improved surgical fastening clip, a method for the production thereof and a method of using the surgical fastening clip. In particular, the surgical fastening clip is formed of a shape memory alloy which provides a clamping force even when the object being clamped shrinks, thins out or moves. The device may change shape to project "teeth" into the object to further enhance its grasping and non-slip capabilities.
2. Description of the Prior Art
Various medical devices formed of shape memory alloys are known in the art. For instance, U.S. Pat. No. 4,170,990 ("Baumgart") discloses a method for implanting and subsequently removing mechanical implants of an alloy which exhibits a memory effect, the implant being removed by cooling it to a temperature below the temperature which actuates the memory effect. Baumgart discloses that such implants can include nails, wires, sutures, clamps, clips, sleeves, rings, discs, pins or tubes. Baumgart further discloses that separation in living tissue can be fixed by rotating, compressing, bending or twisting of the implant by utilization of the memory effect. Accordingly, changes in shape when the implant is used result solely from temperature changes. Baumgart does not disclose a surgical fastening clip of a shape memory alloy which is mechanically deformed such that the legs of the clip clamp an object therebetween.
U.S. Pat. No. 4,665,906 ("Jervis") discloses medical devices of shape memory alloys which exhibit stress-induced martensite at body temperature. In particular, a shape memory alloy at a temperature between M.sub.s and M.sub.d but below A.sub.s is initially, austenitic and application of a stress exceeding .sigma..sub.M forms stress-induced martensite until the alloy becomes fully martensitic, after which application of further stress causes the alloy to deform elastically and then plastically. If the stress-induced martensite is not plastically deformed, release of the stress allows the martensite to recover elastically so as to have zero residual stress but a non-zero residual strain. Heating the alloy above A.sub.s results in reversion to austenite, and if the alloy is unrestrained, the original shape will be recovered. If not, it will be recovered to the extent permitted by the restraint. Upon cooling to the temperature at which the alloy was deformed (or a temperature at which stress-induced martensite is seen), the stress produced by the alloy will be constant. The alloy can thus provide a constant force over a strain range of about 5%.
Alternatively, at a temperature between M.sub.s and M.sub.d but above A.sub.s, upon application of stress the alloy deforms elastically and when the stress exceeds .sigma..sub.m forms stress-induced martensite after which the martensite is deformed, as described above. The unloading behavior is different from that described above in that the alloy recovers elastically at first until an essentially constant critical stress .sigma..sub.A is reached at which point the alloy reverts to austenite without requiring a change in temperature. Then, if the stress is removed from the reverted austenite it recovers elastically. The alloy can thus provide a constant force over an effective working range of about 5%.
Jervis discloses a shape memory alloy ring for holding a sewing cuff to the body of an artificial heart valve. Jervis discloses that such a ring had previously been described as being made in the austenitic state, cooled to the martensitic state, deformed, placed around the valve body and heated to cause reversion to austenite. According to Jervis' invention, the ring is made in the austenitic state, cooled to the martensite phase, expanded, placed around the valve body, heated above A.sub.f and cooled, whereby a constant force is applied to the valve body. Jervis also discloses bone staples, clips, etc. made of a shape memory alloy. In particular, Jervis discloses a staple made of an alloy below A.sub.s which is for holding fragments of bone together, the staples being placed in the martensitic state, heated to the austenitic state and cooled to body temperature to achieve constant force. Above A.sub.s, the staple is held in the deformed position by a moderate force and then released after insertion to provide an accurately-known force. This allows easier removal by deformation which forms stress-induced martensite.
U.S. Pat. No. 4,556,050 ("Hodgson") discloses an artificial sphincter which includes an implantable clamp for selectively pinching closed or opening a vessel in a living body. The clamp includes a spring member and a shape memory member. One of the opening and closing operations is effected by deforming the shape memory member from the memory configuration, and the other of the operations is effected by heat recovering the shape memory member to the memory configuration by heating above body temperatures. Heating is accomplished by means of an ac source via a coil in the shape memory member.
U.S. Pat. No. 4,485,816 ("Krumme") discloses a surgical staple which is formed into a desired closed position at a temperature above the transition temperature and then cooled below the transition temperature before deforming it into an open position, the resulting staple reverting to its closed position when it is subsequently reheated by means of an electrical power supply above the transition temperature, the transition temperature being in the range of 50.degree.-80.degree. C.
Other medical devices of shape memory alloys are disclosed in U.S. Pat. No. 3,786,806 ("Johnson") which discloses a plate formed of a shape memory alloy for drawing fractured bone ends together, U.S. Pat. No. 4,233,690 ("Akins") which discloses a prosthetic element of a shape memory alloy which can be used as a coupling element, U.S. Pat. No. 4,490,112 ("Tanaka") and U.S. Pat. No. 4,037,324 ("Andreasen") which disclose components of shape memory alloys having dental applications, and Soviet Union Publication No. 1,110,447 which discloses a compressing fixator of a shape memory alloy for use in healing bone fractures.
Various types of surgical clips are known in the art. For instance, U.S. Pat. No. 4,844,066 ("Stein"), U.S. Pat. No. 4,834,096 ("Oh"), U.S. Pat. No. 4,696,396 ("Samuels") and U.S. Pat. No. 3,363,628 ("Wood") disclose various types of surgical clips. Five manufacturers sell hemoclips in the United States; such manufacturers include Ethicon (Johnson & Johnson), Weck (Squibb), Richard Allen, Pilling (Japanese) and Auto Suture.
Surgical fastening clips (or hemoclips) are currently used in surgery to prevent bleeding by squeezing vessels and tissue. The clips are left in the body at the conclusion of the operation. Conventional clips are made of malleable stainless steel, titanium or tantalum and are squeezed together on the tissue by plier-like forceps. The metal clip is thus closed by plastic deformation. All of the commercially available clips will frequently slip off the tissue during or shortly after completion of surgery, thereby lessening their effectiveness and decreasing their use to situations wherein a slipping clip is not a vital problem.
The alternative to clipping is suture ligating which is more secure but takes much longer to do. There are many situations wherein all surgeons refuse to use surgical fastening clips because they are not secure enough, and many surgeons simply do not use the clips at all because of their unreliability.
All of the conventionally available clips have some "spring back" when they are squeezed together which then results in the two legs of the clip not lying in opposition but actually having some gap therebetween. Such clips also will not follow tissue as it shrinks in thickness; thus, with such clips there will not be a continuing squeezing force to keep the clip on the tissue. The present invention overcomes a major drawback of the existing clips--their unreliability.